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Willcocks MM, Zaini S, Chamond N, Ulryck N, Allouche D, Rajagopalan N, Davids NA, Fahnøe U, Hadsbjerg J, Rasmussen TB, Roberts LO, Sargueil B, Belsham GJ, Locker N. Distinct roles for the IIId2 sub-domain in pestivirus and picornavirus internal ribosome entry sites. Nucleic Acids Res 2018; 45:13016-13028. [PMID: 29069411 PMCID: PMC5727462 DOI: 10.1093/nar/gkx991] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2017] [Accepted: 10/12/2017] [Indexed: 01/23/2023] Open
Abstract
Viral internal ribosomes entry site (IRES) elements coordinate the recruitment of the host translation machinery to direct the initiation of viral protein synthesis. Within hepatitis C virus (HCV)-like IRES elements, the sub-domain IIId(1) is crucial for recruiting the 40S ribosomal subunit. However, some HCV-like IRES elements possess an additional sub-domain, termed IIId2, whose function remains unclear. Herein, we show that IIId2 sub-domains from divergent viruses have different functions. The IIId2 sub-domain present in Seneca valley virus (SVV), a picornavirus, is dispensable for IRES activity, while the IIId2 sub-domains of two pestiviruses, classical swine fever virus (CSFV) and border disease virus (BDV), are required for 80S ribosomes assembly and IRES activity. Unlike in SVV, the deletion of IIId2 from the CSFV and BDV IRES elements impairs initiation of translation by inhibiting the assembly of 80S ribosomes. Consequently, this negatively affects the replication of CSFV and BDV. Finally, we show that the SVV IIId2 sub-domain is required for efficient viral RNA synthesis and growth of SVV, but not for IRES function. This study sheds light on the molecular evolution of viruses by clearly demonstrating that conserved RNA structures, within distantly related RNA viruses, have acquired different roles in the virus life cycles.
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Affiliation(s)
- Margaret M Willcocks
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford, UK
| | - Salmah Zaini
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford, UK
| | - Nathalie Chamond
- Faculté des Sciences Pharmaceutiques et Biologiques, UMR8015, Université Paris Descartes, Paris, France
| | - Nathalie Ulryck
- Faculté des Sciences Pharmaceutiques et Biologiques, UMR8015, Université Paris Descartes, Paris, France
| | - Delphine Allouche
- Faculté des Sciences Pharmaceutiques et Biologiques, UMR8015, Université Paris Descartes, Paris, France
| | - Noemie Rajagopalan
- Faculté des Sciences Pharmaceutiques et Biologiques, UMR8015, Université Paris Descartes, Paris, France
| | - Nana A Davids
- DTU National Veterinary Institute, Technical University of Denmark, Lindholm, DK-4771 Kalvehave, Denmark
| | - Ulrik Fahnøe
- DTU National Veterinary Institute, Technical University of Denmark, Lindholm, DK-4771 Kalvehave, Denmark
| | - Johanne Hadsbjerg
- DTU National Veterinary Institute, Technical University of Denmark, Lindholm, DK-4771 Kalvehave, Denmark
| | - Thomas Bruun Rasmussen
- DTU National Veterinary Institute, Technical University of Denmark, Lindholm, DK-4771 Kalvehave, Denmark
| | - Lisa O Roberts
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford, UK.,School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, UK
| | - Bruno Sargueil
- Faculté des Sciences Pharmaceutiques et Biologiques, UMR8015, Université Paris Descartes, Paris, France
| | - Graham J Belsham
- DTU National Veterinary Institute, Technical University of Denmark, Lindholm, DK-4771 Kalvehave, Denmark
| | - Nicolas Locker
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford, UK
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Humoud MN, Doyle N, Royall E, Willcocks MM, Sorgeloos F, van Kuppeveld F, Roberts LO, Goodfellow IG, Langereis MA, Locker N. Feline Calicivirus Infection Disrupts Assembly of Cytoplasmic Stress Granules and Induces G3BP1 Cleavage. J Virol 2016; 90:6489-6501. [PMID: 27147742 PMCID: PMC4936126 DOI: 10.1128/jvi.00647-16] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Accepted: 04/27/2016] [Indexed: 12/24/2022] Open
Abstract
UNLABELLED In response to stress such as virus infection, cells can stall translation by storing mRNAs away in cellular compartments called stress granules (SGs). This defense mechanism favors cell survival by limiting the use of energy and nutrients until the stress is resolved. In some cases it may also block viral propagation as viruses are dependent on the host cell resources to produce viral proteins. Human norovirus is a member of the Caliciviridae family responsible for gastroenteritis outbreaks worldwide. Previous studies on caliciviruses have identified mechanisms by which they can usurp the host translational machinery, using the viral protein genome-linked VPg, or regulate host protein synthesis through the mitogen-activated protein kinase (MAPK) pathway. Here, we examined the effect of feline calicivirus (FCV) infection on SG accumulation. We show that FCV infection impairs the assembly of SGs despite an increased phosphorylation of eukaryotic initiation factor eIF2α, a hallmark of stress pathway activation. Furthermore, SGs did not accumulate in FCV-infected cells that were stressed with arsenite or hydrogen peroxide. FCV infection resulted in the cleavage of the SG-nucleating protein Ras-GTPase activating SH3 domain-binding protein (G3BP1), which is mediated by the viral 3C-like proteinase NS6(Pro) Using mutational analysis, we identified the FCV-induced cleavage site within G3BP1, which differs from the poliovirus 3C proteinase cleavage site previously identified. Finally, we showed that NS6(Pro)-mediated G3BP1 cleavage impairs SG assembly. In contrast, murine norovirus (MNV) infection did not impact arsenite-induced SG assembly or G3BP1 integrity, suggesting that related caliciviruses have distinct effects on the stress response pathway. IMPORTANCE Human noroviruses are a major cause of viral gastroenteritis, and it is important to understand how they interact with the infected host cell. Feline calicivirus (FCV) and murine norovirus (MNV) are used as models to understand norovirus biology. Recent studies have suggested that the assembly of stress granules is central in orchestrating stress and antiviral responses to restrict viral replication. Overall, our study provides the first insight on how caliciviruses impair stress granule assembly by targeting the nucleating factor G3BP1 via the viral proteinase NS6(Pro) This work provides new insights into host-pathogen interactions that regulate stress pathways during FCV infection.
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Affiliation(s)
- Majid N Humoud
- University of Surrey, Faculty of Health and Medical Sciences, School of Biosciences and Medicine, Guildford, United Kingdom
| | - Nicole Doyle
- University of Surrey, Faculty of Health and Medical Sciences, School of Biosciences and Medicine, Guildford, United Kingdom
| | - Elizabeth Royall
- University of Surrey, Faculty of Health and Medical Sciences, School of Biosciences and Medicine, Guildford, United Kingdom
| | - Margaret M Willcocks
- University of Surrey, Faculty of Health and Medical Sciences, School of Biosciences and Medicine, Guildford, United Kingdom
| | - Frederic Sorgeloos
- Division of Virology, Department of Pathology, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge, United Kingdom
| | - Frank van Kuppeveld
- Virology Division, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
| | - Lisa O Roberts
- University of Surrey, Faculty of Health and Medical Sciences, School of Biosciences and Medicine, Guildford, United Kingdom
| | - Ian G Goodfellow
- Division of Virology, Department of Pathology, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge, United Kingdom
| | - Martijn A Langereis
- Virology Division, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
| | - Nicolas Locker
- University of Surrey, Faculty of Health and Medical Sciences, School of Biosciences and Medicine, Guildford, United Kingdom
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Royall E, Doyle N, Abdul-Wahab A, Emmott E, Morley SJ, Goodfellow I, Roberts LO, Locker N. Murine norovirus 1 (MNV1) replication induces translational control of the host by regulating eIF4E activity during infection. J Biol Chem 2015; 290:4748-4758. [PMID: 25561727 PMCID: PMC4335213 DOI: 10.1074/jbc.m114.602649] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Protein synthesis is a tightly controlled process responding to several stimuli, including viral infection. As obligate intracellular parasites, viruses depend on the translation machinery of the host and can manipulate it by affecting the availability and function of specific eukaryotic initiation factors (eIFs). Human norovirus is a member of the Caliciviridae family and is responsible for gastroenteritis outbreaks. Previous studies on feline calicivirus and murine norovirus 1 (MNV1) demonstrated that the viral protein, genome-linked (VPg), acts to direct translation by hijacking the host protein synthesis machinery. Here we report that MNV1 infection modulates the MAPK pathway to activate eIF4E phosphorylation. Our results show that the activation of p38 and Mnk during MNV1 infection is important for MNV1 replication. Furthermore, phosphorylated eIF4E relocates to the polysomes, and this contributes to changes in the translational state of specific host mRNAs. We propose that global translational control of the host by eIF4E phosphorylation is a key component of the host-pathogen interaction.
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Affiliation(s)
- Elizabeth Royall
- University of Surrey, Faculty of Health and Medical Sciences, School of Biosciences and Medicine, Guildford GU2 7HX, United Kingdom
| | - Nicole Doyle
- University of Surrey, Faculty of Health and Medical Sciences, School of Biosciences and Medicine, Guildford GU2 7HX, United Kingdom
| | - Azimah Abdul-Wahab
- University of Surrey, Faculty of Health and Medical Sciences, School of Biosciences and Medicine, Guildford GU2 7HX, United Kingdom
| | - Ed Emmott
- Division of Virology, Department of Pathology, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, United Kingdom
| | - Simon J Morley
- Department of Biochemistry and Molecular Biology, School of Life Sciences, University of Sussex, JMS Building, Brighton BN1 9RH, United Kingdom
| | - Ian Goodfellow
- Division of Virology, Department of Pathology, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, United Kingdom
| | - Lisa O Roberts
- University of Surrey, Faculty of Health and Medical Sciences, School of Biosciences and Medicine, Guildford GU2 7HX, United Kingdom
| | - Nicolas Locker
- University of Surrey, Faculty of Health and Medical Sciences, School of Biosciences and Medicine, Guildford GU2 7HX, United Kingdom.
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Othman Z, Sulaiman MK, Willcocks MM, Ulryck N, Blackbourn DJ, Sargueil B, Roberts LO, Locker N. Functional analysis of Kaposi's sarcoma-associated herpesvirus vFLIP expression reveals a new mode of IRES-mediated translation. RNA 2014; 20:1803-1814. [PMID: 25246653 PMCID: PMC4201831 DOI: 10.1261/rna.045328.114] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/17/2014] [Accepted: 08/26/2014] [Indexed: 06/03/2023]
Abstract
Kaposi's sarcoma-associated herpesvirus (KSHV) is an oncogenic virus, the etiological agent of Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL). One of the key viral proteins that contributes to tumorigenesis is vFLIP, a viral homolog of the FLICE inhibitory protein. This KSHV protein interacts with the NFκB pathway to trigger the expression of antiapoptotic and proinflammatory genes and ultimately leads to tumor formation. The expression of vFLIP is regulated at the translational level by an internal ribosomal entry site (IRES) element. However, the precise mechanism by which ribosomes are recruited internally and the exact location of the IRES has remained elusive. Here we show that a 252-nt fragment directly upstream of vFLIP, within a coding region, directs translation. We have established its RNA structure and demonstrate that IRES activity requires the presence of eIF4A and an intact eIF4G. Furthermore, and unusually for an IRES, eIF4E is part of the complex assembled onto the vFLIP IRES to direct translation. These molecular interactions define a new paradigm for IRES-mediated translation.
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Affiliation(s)
- Zulkefley Othman
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
| | - Mariam K Sulaiman
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
| | - Margaret M Willcocks
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
| | - Nathalie Ulryck
- Faculté des Sciences Pharmaceutiques et Biologiques, UMR8015, Université Paris Descartes, 75270 Paris, France
| | - David J Blackbourn
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
| | - Bruno Sargueil
- Faculté des Sciences Pharmaceutiques et Biologiques, UMR8015, Université Paris Descartes, 75270 Paris, France
| | - Lisa O Roberts
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
| | - Nicolas Locker
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
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Chung L, Bailey D, Leen EN, Emmott EP, Chaudhry Y, Roberts LO, Curry S, Locker N, Goodfellow IG. Norovirus translation requires an interaction between the C Terminus of the genome-linked viral protein VPg and eukaryotic translation initiation factor 4G. J Biol Chem 2014; 289:21738-50. [PMID: 24928504 PMCID: PMC4118132 DOI: 10.1074/jbc.m114.550657] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Viruses have evolved a variety of mechanisms to usurp the host cell translation machinery to enable translation of the viral genome in the presence of high levels of cellular mRNAs. Noroviruses, a major cause of gastroenteritis in man, have evolved a mechanism that relies on the interaction of translation initiation factors with the virus-encoded VPg protein covalently linked to the 5′ end of the viral RNA. To further characterize this novel mechanism of translation initiation, we have used proteomics to identify the components of the norovirus translation initiation factor complex. This approach revealed that VPg binds directly to the eIF4F complex, with a high affinity interaction occurring between VPg and eIF4G. Mutational analyses indicated that the C-terminal region of VPg is important for the VPg-eIF4G interaction; viruses with mutations that alter or disrupt this interaction are debilitated or non-viable. Our results shed new light on the unusual mechanisms of protein-directed translation initiation.
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Affiliation(s)
- Liliane Chung
- From the Section of Virology, Department of Medicine, Imperial College London, Norfolk Place, London W2 1PG, United Kingdom
| | - Dalan Bailey
- From the Section of Virology, Department of Medicine, Imperial College London, Norfolk Place, London W2 1PG, United Kingdom, School of Immunity and Infection, College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, United Kingdom
| | - Eoin N Leen
- Department of Life Sciences, Imperial College London, South Kensington, London SW7 2AZ, United Kingdom
| | - Edward P Emmott
- Division of Virology, Department of Pathology, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, United Kingdom, and
| | - Yasmin Chaudhry
- From the Section of Virology, Department of Medicine, Imperial College London, Norfolk Place, London W2 1PG, United Kingdom, Division of Virology, Department of Pathology, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, United Kingdom, and
| | - Lisa O Roberts
- University of Surrey, Faculty of Health and Medical Sciences, School of Biosciences and Medicine, Guildford GU2 7HX, United Kingdom
| | - Stephen Curry
- Department of Life Sciences, Imperial College London, South Kensington, London SW7 2AZ, United Kingdom
| | - Nicolas Locker
- University of Surrey, Faculty of Health and Medical Sciences, School of Biosciences and Medicine, Guildford GU2 7HX, United Kingdom
| | - Ian G Goodfellow
- From the Section of Virology, Department of Medicine, Imperial College London, Norfolk Place, London W2 1PG, United Kingdom, Division of Virology, Department of Pathology, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, United Kingdom, and
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Brödel AK, Sonnabend A, Roberts LO, Stech M, Wüstenhagen DA, Kubick S. IRES-mediated translation of membrane proteins and glycoproteins in eukaryotic cell-free systems. PLoS One 2013; 8:e82234. [PMID: 24376523 PMCID: PMC3869664 DOI: 10.1371/journal.pone.0082234] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Accepted: 10/22/2013] [Indexed: 02/04/2023] Open
Abstract
Internal ribosome entry site (IRES) elements found in the 5′ untranslated region of mRNAs enable translation initiation in a cap-independent manner, thereby representing an alternative to cap-dependent translation in cell-free protein expression systems. However, IRES function is largely species-dependent so their utility in cell-free systems from different species is rather limited. A promising approach to overcome these limitations would be the use of IRESs that are able to recruit components of the translation initiation apparatus from diverse origins. Here, we present a solution to this technical problem and describe the ability of a number of viral IRESs to direct efficient protein expression in different eukaryotic cell-free expression systems. The IRES from the intergenic region (IGR) of the Cricket paralysis virus (CrPV) genome was shown to function efficiently in four different cell-free systems based on lysates derived from cultured Sf21, CHO and K562 cells as well as wheat germ. Our results suggest that the CrPV IGR IRES-based expression vector is universally applicable for a broad range of eukaryotic cell lysates. Sf21, CHO and K562 cell-free expression systems are particularly promising platforms for the production of glycoproteins and membrane proteins since they contain endogenous microsomes that facilitate the incorporation of membrane-spanning proteins and the formation of post-translational modifications. We demonstrate the use of the CrPV IGR IRES-based expression vector for the enhanced synthesis of various target proteins including the glycoprotein erythropoietin and the membrane proteins heparin-binding EGF-like growth factor receptor as well as epidermal growth factor receptor in the above mentioned eukaryotic cell-free systems. CrPV IGR IRES-mediated translation will facilitate the development of novel eukaryotic cell-free expression platforms as well as the high-yield synthesis of desired proteins in already established systems.
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Affiliation(s)
- Andreas K. Brödel
- Fraunhofer Institute for Biomedical Engineering (IBMT) Branch Potsdam-Golm, Potsdam, Germany
| | - Andrei Sonnabend
- Fraunhofer Institute for Biomedical Engineering (IBMT) Branch Potsdam-Golm, Potsdam, Germany
| | - Lisa O. Roberts
- Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom
| | - Marlitt Stech
- Fraunhofer Institute for Biomedical Engineering (IBMT) Branch Potsdam-Golm, Potsdam, Germany
| | - Doreen A. Wüstenhagen
- Fraunhofer Institute for Biomedical Engineering (IBMT) Branch Potsdam-Golm, Potsdam, Germany
| | - Stefan Kubick
- Fraunhofer Institute for Biomedical Engineering (IBMT) Branch Potsdam-Golm, Potsdam, Germany
- * E-mail:
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Wiley MR, Roberts LO, Adelman ZN, Myles KM. Double subgenomic alphaviruses expressing multiple fluorescent proteins using a Rhopalosiphum padi virus internal ribosome entry site element. PLoS One 2010; 5:e13924. [PMID: 21085714 PMCID: PMC2978087 DOI: 10.1371/journal.pone.0013924] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2010] [Accepted: 10/12/2010] [Indexed: 12/22/2022] Open
Abstract
Double subgenomic Sindbis virus (dsSINV) vectors are widely used for the expression of proteins, peptides, and RNA sequences. These recombinant RNA viruses permit high level expression of a heterologous sequence in a wide range of animals, tissues, and cells. However, the alphavirus genome structure and replication strategy is not readily amenable to the expression of more than one heterologous sequence. The Rhopalosiphum padi virus (RhPV) genome contains two internal ribosome entry site (IRES) elements that mediate cap-independent translation of the virus nonstructural and structural proteins. Most IRES elements that have been characterized function only in mammalian cells but previous work has shown that the IRES element present in the 5′ untranslated region (UTR) of the RhPV genome functions efficiently in mammalian, insect, and plant systems. To determine if the 5′ RhPV IRES element could be used to express more than one heterologous sequence from a dsSINV vector, RhPV 5′ IRES sequences were placed between genes for two different fluorescent marker proteins in the dsSINV, TE/3′2J/mcs. While mammalian and insect cells infected with recombinant viruses containing the RhPV sequences expressed both fluorescent marker proteins, only single marker proteins were routinely observed in cells infected with dsSINV vectors in which the RhPV IRES had been replaced by a luciferase fragment, an antisense RhPV IRES, or no intergenic sequence. Thus, we report development of a versatile tool for the expression of multiple sequences in diverse cell types.
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Affiliation(s)
- Michael R. Wiley
- Fralin Life Science Institute, Department of Entomology, Virginia Tech, Blacksburg, Virginia, United States of America
| | - Lisa O. Roberts
- Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom
| | - Zach N. Adelman
- Fralin Life Science Institute, Department of Entomology, Virginia Tech, Blacksburg, Virginia, United States of America
| | - Kevin M. Myles
- Fralin Life Science Institute, Department of Entomology, Virginia Tech, Blacksburg, Virginia, United States of America
- * E-mail:
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8
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Gerondopoulos A, Jackson T, Monaghan P, Doyle N, Roberts LO. Murine norovirus-1 cell entry is mediated through a non-clathrin-, non-caveolae-, dynamin- and cholesterol-dependent pathway. J Gen Virol 2010; 91:1428-38. [PMID: 20147520 DOI: 10.1099/vir.0.016717-0] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
For many viruses, endocytosis and exposure to the low pH within acidic endosomes is essential for infection. It has previously been reported that feline calicivirus uses clathrin-mediated endocytosis for entry into mammalian cells. Here, we report that infection of RAW264.7 macrophages by the closely related murine norovirus-1 (MNV-1) does not require the clathrin pathway, as infection was not inhibited by expression of dominant-negative Eps15 or by knockdown of the adaptin-2 complex. Further, infection was not inhibited by reagents that raise endosomal pH. RAW264.7 macrophages were shown not to express caveolin, and flotillin depletion did not inhibit infection, suggesting that caveolae and the flotillin pathway are not required for cell entry. However, MNV-1 infection was inhibited by methyl-beta-cyclodextrin and the dynamin inhibitor, dynasore. Addition of these drugs to the cells after a period of virus internalization did not inhibit infection, suggesting the involvement of cholesterol-sensitive lipid rafts and dynamin in the entry mechanism. Macropinocytosis (MPC) was shown to be active in RAW264.7 macrophages (as indicated by uptake of dextran) and could be blocked by 5-(N-ethyl-N-isopropyl) amiloride (EIPA), which is reported to inhibit this pathway. However, infection was enhanced in the presence of EIPA. Similarly, actin disruption, which also inhibits MPC, resulted in enhanced infection. These results suggest that MPC could contribute to virus degradation or that inhibition of MPC could lead to the upregulation of other endocytic pathways of virus uptake.
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Affiliation(s)
- Andreas Gerondopoulos
- Faculty of Health and Medical Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
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9
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Abstract
Viruses do not carry their own protein biosynthesis machinery and the translation of viral proteins therefore requires that the virus usurps the machinery of the host cell. To allow optimal translation of viral proteins at the expense of cellular proteins, virus families have evolved a variety of methods to repress the host translation machinery, while allowing effective viral protein synthesis. Many viruses use noncanonical mechanisms that permit translation of their own RNAs under these conditions. Viruses have also developed mechanisms to evade host innate immune responses that would repress translation under conditions of viral infection, in particular PKR activation in response to double-stranded RNA (dsRNA). Importantly, the study of viral translation mechanisms has enormously enhanced our understanding of many aspects of the cellular protein biosynthesis pathway and its components. A number of unusual mechanisms of translation initiation that were first discovered in viruses have since been observed in cellular mRNAs, and it has become apparent that a diverse range of translation mechanisms operates in eukaryotes, allowing subtle regulation of this essential process.
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Affiliation(s)
- Lisa O Roberts
- Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom
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10
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Belsham GJ, Nielsen I, Normann P, Royall E, Roberts LO. Monocistronic mRNAs containing defective hepatitis C virus-like picornavirus internal ribosome entry site elements in their 5' untranslated regions are efficiently translated in cells by a cap-dependent mechanism. RNA 2008; 14:1671-1680. [PMID: 18567818 PMCID: PMC2491466 DOI: 10.1261/rna.1039708] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2008] [Accepted: 05/07/2008] [Indexed: 05/26/2023]
Abstract
The initiation of protein synthesis on mRNAs within eukaryotic cells is achieved either by a 5' cap-dependent mechanism or through internal initiation directed by an internal ribosome entry site (IRES). Picornavirus IRES elements, located in the 5' untranslated region (5'UTR), contain extensive secondary structure and multiple upstream AUG codons. These features can be expected to inhibit cap-dependent initiation of translation. However, we have now shown that certain mutant hepatitis C virus-like picornavirus IRES elements (from porcine teschovirus-1 and avian encephalomyelitis virus), which are unable to direct internal initiation, are not significant barriers to efficient translation of capped monocistronic mRNAs that contain these defective elements within their 5'UTRs. Moreover, the translation of these mRNAs is highly sensitive to the expression of an enterovirus 2A protease (which induces cleavage of eIF4G) and is also inhibited by hippuristanol, a specific inhibitor of eIF4A function, in contrast to their parental wild-type IRES elements. These results provide a possible basis for the evolution of viral IRES elements within the context of functional mRNAs that are translated by a cap-dependent mechanism.
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Affiliation(s)
- Graham J Belsham
- National Veterinary Institute, Technical University of Denmark, Lindholm, DK-4771, Kalvehave, Denmark.
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Monie TP, Perrin AJ, Birtley JR, Sweeney TR, Karakasiliotis I, Chaudhry Y, Roberts LO, Matthews S, Goodfellow IG, Curry S. Structural insights into the transcriptional and translational roles of Ebp1. EMBO J 2007; 26:3936-44. [PMID: 17690690 PMCID: PMC1994118 DOI: 10.1038/sj.emboj.7601817] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2007] [Accepted: 07/11/2007] [Indexed: 11/08/2022] Open
Abstract
The ErbB3-binding protein 1 (Ebp1) is an important regulator of transcription, affecting eukaryotic cell growth, proliferation, differentiation and survival. Ebp1 can also affect translation and cooperates with the polypyrimidine tract-binding protein (PTB) to stimulate the activity of the internal ribosome entry site (IRES) of foot-and-mouth disease virus (FMDV). We report here the crystal structure of murine Ebp1 (p48 isoform), providing the first glimpse of the architecture of this versatile regulator. The structure reveals a core domain that is homologous to methionine aminopeptidases, coupled to a C-terminal extension that contains important motifs for binding proteins and RNA. It sheds new light on the conformational differences between the p42 and p48 isoforms of Ebp1, the disposition of the key protein-interacting motif ((354)LKALL(358)) and the RNA-binding activity of Ebp1. We show that the primary RNA-binding site is formed by a Lys-rich motif in the C terminus and mediates the interaction with the FMDV IRES. We also demonstrate a specific functional requirement for Ebp1 in FMDV IRES-directed translation that is independent of a direct interaction with PTB.
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Affiliation(s)
- Tom P Monie
- Division of Cell and Molecular Biology, Imperial College, South Kensington Campus, London, UK
| | - Andrew J Perrin
- Division of Cell and Molecular Biology, Imperial College, South Kensington Campus, London, UK
| | - James R Birtley
- Division of Cell and Molecular Biology, Imperial College, South Kensington Campus, London, UK
| | - Trevor R Sweeney
- Division of Cell and Molecular Biology, Imperial College, South Kensington Campus, London, UK
| | | | - Yasmin Chaudhry
- Department of Virology, Faculty of Medicine, Imperial College London, London, UK
| | - Lisa O Roberts
- School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey, UK
| | | | - Ian G Goodfellow
- Department of Virology, Faculty of Medicine, Imperial College London, London, UK
| | - Stephen Curry
- Division of Cell and Molecular Biology, Imperial College, South Kensington Campus, London, UK
- Division of Cell and Molecular Biology, Imperial College, South Kensington Campus, London SW7 2AZ, UK. Tel.: +44 20 7594 7632; Fax: +44 20 7589 0191; E-mail:
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12
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Groppelli E, Belsham GJ, Roberts LO. Identification of minimal sequences of the Rhopalosiphum padi virus 5' untranslated region required for internal initiation of protein synthesis in mammalian, plant and insect translation systems. J Gen Virol 2007; 88:1583-1588. [PMID: 17412990 DOI: 10.1099/vir.0.82682-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Rhopalosiphum padi virus (RhPV) is a member of the family Dicistroviridae. The genomes of viruses in this family contain two open reading frames, each preceded by distinct internal ribosome entry site (IRES) elements. The RhPV 5' IRES is functional in mammalian, insect and plant translation systems and can form 48S initiation complexes in vitro with just the mammalian initiation factors eIF2, eIF3 and eIF1. Large regions of the 5' untranslated region (UTR) can be deleted without affecting initiation-complex formation. The minimal sequences required for directing internal initiation in mammalian (rabbit reticulocyte lysate), plant (wheatgerm extract) and insect (Sf21 cells) translation systems have now been defined. A fragment (nt 426-579) from the 3' portion of the 5' UTR can direct translation in each of these translation systems. In addition, a distinct region (nt 300-429) is also active. Thus, unstructured regions within the 5' UTR seem to be critical for IRES function.
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Affiliation(s)
- Elisabetta Groppelli
- School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
| | - Graham J Belsham
- BBSRC Institute for Animal Health, Ash Road, Pirbright, Surrey GU24 0NF, UK
| | - Lisa O Roberts
- School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
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13
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Karakasiliotis I, Chaudhry Y, Roberts LO, Goodfellow IG. Feline calicivirus replication: requirement for polypyrimidine tract-binding protein is temperature-dependent. J Gen Virol 2006; 87:3339-3347. [PMID: 17030868 DOI: 10.1099/vir.0.82153-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The interaction of host-cell nucleic acid-binding proteins with the genomes of positive-stranded RNA viruses is known to play a role in the translation and replication of many viruses. To date, however, the characterization of similar interactions with the genomes of members of the family Caliciviridae has been limited to in vitro binding analysis. In this study, Feline calicivirus (FCV) has been used as a model system to identify and characterize the role of host-cell factors that interact with the viral RNA. It was demonstrated that polypyrimidine tract-binding protein (PTB) interacts specifically with the 5' sequences of the FCV genomic and subgenomic RNAs. Using RNA interference it was shown that PTB is required for efficient FCV replication in a temperature-dependent manner. siRNA-mediated knockdown of PTB resulted in a 15- to 100-fold reduction in virus titre, as well as a concomitant reduction in viral RNA and protein synthesis at 32 degrees C. In addition, virus-induced cytopathic effect was significantly delayed as a result of an siRNA-mediated reduction in PTB levels. A role for PTB in the calicivirus life cycle was more apparent at temperatures above and below 37 degrees C, fitting with the hypothesis that PTB functions as an RNA chaperone, potentially aiding the folding of RNA into functional structures. This is the first functional demonstration of a host-cell protein interacting with a calicivirus RNA.
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Affiliation(s)
- Ioannis Karakasiliotis
- Department of Virology, Faculty of Medicine, Imperial College London, St Mary's Campus, Norfolk Place, London W2 1PG, UK
| | - Yasmin Chaudhry
- Department of Virology, Faculty of Medicine, Imperial College London, St Mary's Campus, Norfolk Place, London W2 1PG, UK
| | - Lisa O Roberts
- School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
| | - Ian G Goodfellow
- Department of Virology, Faculty of Medicine, Imperial College London, St Mary's Campus, Norfolk Place, London W2 1PG, UK
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14
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Chaudhry Y, Nayak A, Bordeleau ME, Tanaka J, Pelletier J, Belsham GJ, Roberts LO, Goodfellow IG. Caliciviruses differ in their functional requirements for eIF4F components. J Biol Chem 2006; 281:25315-25. [PMID: 16835235 DOI: 10.1074/jbc.m602230200] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Two classes of viruses, namely members of the Potyviridae and Caliciviridae, use a novel mechanism for the initiation of protein synthesis that involves the interaction of translation initiation factors with a viral protein covalently linked to the viral RNA, known as VPg. The calicivirus VPg proteins can interact directly with the initiation factors eIF4E and eIF3. Translation initiation on feline calicivirus (FCV) RNA requires eIF4E because it is inhibited by recombinant 4E-BP1. However, to date, there have been no functional studies carried out with respect to norovirus translation initiation, because of a lack of a suitable source of VPg-linked viral RNA. We have now used the recently identified murine norovirus (MNV) as a model system for norovirus translation and have extended our previous studies with FCV RNA to examine the role of the other eIF4F components in translation initiation. We now demonstrate that, as with FCV, MNV VPg interacts directly with eIF4E, although, unlike FCV RNA, translation of MNV RNA is not sensitive to 4E-BP1, eIF4E depletion, or foot-and-mouth disease virus Lb protease-mediated cleavage of eIF4G. We also demonstrate that both FCV and MNV RNA translation require the RNA helicase component of the eIF4F complex, namely eIF4A, because translation was sensitive (albeit to different degrees) to a dominant negative form and to a small molecule inhibitor of eIF4A (hippuristanol). These results suggest that calicivirus RNAs differ with respect to their requirements for the components of the eIF4F translation initiation complex.
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Affiliation(s)
- Yasmin Chaudhry
- Department of Virology, Faculty of Medicine, Imperial College London, St. Mary's Campus, Norfolk Place, London W2 1PG, United Kingdom
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15
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Abstract
Feline calicivirus (FCV) belongs to the family Caliciviridae and is an important pathogen of the upper respiratory tract of cats. Recent studies have shown that cells infected with FCV undergo apoptosis, as evidenced by caspase activation, chromatin condensation and cleavage of poly(ADP-ribose) polymerase. Here, the upstream events were investigated in order to define the molecular mechanism of apoptosis in FCV-infected cells. It was shown that FCV induced translocation of phosphatidylserine to the cell outer membrane and release of cytochrome c from mitochondria at about 6-8 h post-infection. These events were preceded by the loss of mitochondrial membrane potential and Bax translocation from the cytosol to mitochondria between 4 and 6 h after infection. Release of cytochrome c from mitochondria triggered the activation of caspase-9 and the subsequent activation of the executioner caspase, caspase-3. These results suggest that the mitochondrial pathway of apoptosis is triggered during FCV infection.
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Affiliation(s)
- Alessandro Natoni
- School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
| | - George E N Kass
- School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
| | - Michael J Carter
- School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
| | - Lisa O Roberts
- School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
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16
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Pijlman GP, Roode EC, Fan X, Roberts LO, Belsham GJ, Vlak JM, van Oers MM. Stabilized baculovirus vector expressing a heterologous gene and GP64 from a single bicistronic transcript. J Biotechnol 2005; 123:13-21. [PMID: 16364483 DOI: 10.1016/j.jbiotec.2005.10.022] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2005] [Revised: 10/04/2005] [Accepted: 10/24/2005] [Indexed: 11/20/2022]
Abstract
The efficient scale-up of recombinant protein production in insect-cell bioreactors using baculovirus expression vectors is hampered by reductions in yield with increasing viral passage, the so-called passage effect. This phenomenon is characterized by the generation and subsequent accumulation of defective interfering baculoviruses (DIs), which interfere with the replication of genomically intact virus. A novel baculovirus expression vector is presented equipped with a bicistronic expression cassette that allows the simultaneous expression of the recombinant gene (GFP, first cistron) and an essential baculovirus gene (GP64, second cistron) from a single messenger RNA (mRNA). The translation of GP64 is mediated by an internal ribosome entry site (IRES) element from Rhopalosiphum padi virus (RhPV) while the native GP64 gene is deleted. In this way, a dominant selection pressure is placed on the entire bicistronic mRNA and hence on the maintenance of the foreign gene. The bicistronic expression vector was superior to the control baculovirus vector in that GFP expression remained at much higher levels upon continued virus passage. The versatility of this stabilized vector was demonstrated by its ability to propagate in a number of cell lines including Sf21, Sf9 and High Five cells. This novel baculovirus vector is especially valuable for large-scale recombinant protein production in insect-cell bioreactors where the number of viral passages is high.
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Affiliation(s)
- Gorben P Pijlman
- Laboratory of Virology, Wageningen University, Binnenhaven 11, 6709 PD Wageningen, The Netherlands
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17
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Terenin IM, Dmitriev SE, Andreev DE, Royall E, Belsham GJ, Roberts LO, Shatsky IN. A cross-kingdom internal ribosome entry site reveals a simplified mode of internal ribosome entry. Mol Cell Biol 2005; 25:7879-88. [PMID: 16107731 PMCID: PMC1190281 DOI: 10.1128/mcb.25.17.7879-7888.2005] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Rhopalosiphum padi virus (RhPV) is an insect virus of the Dicistroviridae family. Recently, the 579-nucleotide-long 5' untranslated region (UTR) of RhPV has been shown to contain an internal ribosome entry site (IRES) that functions efficiently in mammalian, plant, and insect in vitro translation systems. Here, the mechanism of action of the RhPV IRES has been characterized by reconstitution of mammalian 48S initiation complexes on the IRES from purified components combined with the toeprint assay. There is an absolute requirement for the initiation factors eIF2 and eIF3 and the scanning factor eIF1 to form 48S complexes on the IRES. In addition, eIF1A, eIF4F (or the C-terminal fragment of eIF4G), and eIF4A strongly stimulated the assembly of this complex, whereas eIF4B had no effect. Although the eIF4-dependent pathway is dominant in the RhPV IRES-directed cell-free translation, omission of either eIF4G or eIF4A or both still allowed the assembly of 48S complexes from purified components with approximately 23% of maximum efficiency. Deletions of up to 100 nucleotides throughout the 5'-UTR sequence produced at most a marginal effect on the IRES activity, suggesting the absence of specific binding sites for initiation factors. Only deletion of the U-rich unstructured 380-nucleotide region proximal to the initiation codon resulted in a complete loss of the IRES activity. We suggest that the single-stranded nature of the RhPV IRES accounts for its strong but less selective potential to bind key mRNA recruiting components of the translation initiation apparatus from diverse origins.
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Affiliation(s)
- Ilya M Terenin
- Belozersky Institute of Physico-Chemical Biology, Moscow State University, Russian Federation
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18
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Abstract
Caliciviruses are important pathogens of man and animals; feline calicivirus (FCV) is responsible for an acute upper respiratory tract disease in cats. To date, little is known about the mechanism of cell damage induced by these viruses. We set out to determine if apoptosis played any role in cell death in FCV infection of cultured cells. We demonstrate that caspase-2, -3, and -7 were activated during FCV infection, as evidenced by pro-form processing and an increase in acetyl-Asp-Glu-Val-Asp-7-amido-4-trifluoromethylcoumarin cleavage activity, as well as cleavage of poly(ADP-ribose)polymerase. Caspase activation coincided with the condensation of chromatin. At about 8 h post infection we also detected cleavage of the FCV capsid protein; this was prevented by caspase inhibitors. Taken together these results suggest that FCV triggers apoptosis within infected cells and that caspases are involved in the cleavage of the capsid protein.
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Affiliation(s)
- Lisa O Roberts
- School of Biomedical and Life Sciences, University of Surrey, Guildford, GU2 7XH, United Kingdom
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19
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Willcocks MM, Carter MJ, Roberts LO. Cleavage of eukaryotic initiation factor eIF4G and inhibition of host-cell protein synthesis during feline calicivirus infection. J Gen Virol 2004; 85:1125-1130. [PMID: 15105529 DOI: 10.1099/vir.0.19564-0] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Caliciviruses are small, non-enveloped, positive-stranded RNA viruses that are pathogenic for both animals and man. Although their capsid structure and genomic organization are distinct from picornaviruses, they have similarities to these viruses in their non-structural proteins. Picornaviruses induce a rapid inhibition of host-cell cap-dependent protein synthesis and this is mainly achieved through cleavage of eIF4G and/or dephosphorylation of 4E-BP1. In this study, the effect of calicivirus infection was examined on host-cell protein synthesis in order to determine whether they also induce host shut-off. We report that infection of cells with feline calicivirus (FCV) leads to the inhibition of cellular protein synthesis. This is accompanied by the cleavage of the eukaryotic translation initiation factors eIF4GI and eIF4GII in a manner reminiscent of that induced by picornaviruses. However, the cleavages occur at different sites. The potential mechanisms of these cleavage events and the implications for the translation of calicivirus mRNA are discussed.
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Affiliation(s)
- Margaret M Willcocks
- School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
| | - Michael J Carter
- School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
| | - Lisa O Roberts
- School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
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20
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Abstract
Artificial minigenomes are powerful tools for studying the replication and transcription of negative-strand RNA viruses. Bunyamwera virus (BUN; genus Orthobunyavirus, family Bunyaviridae) is an arbovirus that shows fundamental biological differences when replicating in mammalian versus mosquito cells. To study BUN RNA synthesis in mosquito cells, we developed a bacteriophage T7 RNA polymerase-based minireplicon system similar to that described previously for mammalian cells. An Aedes albopictus C6/36-derived mosquito cell line stably expressing T7 RNA polymerase was established. Viral proteins and artificial minigenomes (containing Renilla luciferase as a reporter) were transcribed and expressed in these cells from transfected T7 promoter-containing plasmids. Transcription of the minigenome required two viral proteins, the nucleocapsid protein N and the RNA-dependent RNA polymerase L, a situation similar to that in mammalian cells. However, unlike the situation in mammalian cells, the viral polymerase was not inhibited by the viral nonstructural protein NSs. We also report that promoter strength is different for vertebrate versus invertebrate cells. The development of this system opens the way for a detailed comparison of bunyavirus replication in cells of disparate phylogeny.
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Affiliation(s)
- Alain Kohl
- Institute of Virology, University of Glasgow, Church Street, Glasgow G11 5JR, Scotland, United Kingdom
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21
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Royall E, Woolaway KE, Schacherl J, Kubick S, Belsham GJ, Roberts LO. The Rhopalosiphum padi virus 5′ internal ribosome entry site is functional in Spodoptera frugiperda 21 cells and in their cell-free lysates: implications for the baculovirus expression system. J Gen Virol 2004; 85:1565-1569. [PMID: 15166440 DOI: 10.1099/vir.0.79992-0] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cap-independent internal initiation of translation occurs on a number of viral and cellular mRNAs and is directed by internal ribosome entry site (IRES) elements. Rhopalosiphum padi virus (RhPV) is a member of the Dicistroviridae. These viruses have single-stranded, positive-sense RNA genomes that contain two open reading frames, both preceded by IRES elements. Previously, the activity of the RhPV 5′ UTR IRES has been demonstrated in mammalian, Drosophila and wheat germ in vitro translation systems. It is now shown that this IRES also functions within Spodoptera frugiperda (Sf21) cells which are widely used in the baculovirus expression system, and in a novel Sf21 cell-based lysate system. Inclusion of the RhPV IRES in a dicistronic reporter mRNA transcript increased translation of the second cistron 23-fold within Sf21 cells. In contrast, the encephalomyocarditis virus IRES was inactive in both systems. The RhPV IRES therefore has the potential to be utilized in insect cell expression systems.
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Affiliation(s)
- Elizabeth Royall
- School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
| | - Kathryn E Woolaway
- School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
| | | | | | - Graham J Belsham
- BBSRC Institute for Animal Health, Ash Road, Pirbright, Woking, Surrey GU24 0NF, UK
| | - Lisa O Roberts
- School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
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22
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Abstract
Feline calicivirus (FCV) is responsible for an acute upper respiratory tract disease in cats. The FCV capsid protein is synthesized as a precursor (76 kDa) that is post-translationally processed into the mature 62 kDa capsid protein by removal of the N-terminal 124 amino acids. Our previous studies have also detected a 40 kDa protein, related to the FCV capsid protein, produced during infection. Here we demonstrate that cleavage of the FCV capsid protein, during infection of cells in culture, was prevented by caspase inhibitors. In addition, caspase-2, -3 and -7 were activated during FCV infection, as shown by pro-form processing, an increase in N-acetyl-Asp-Glu-Val-Asp-7-amido-4-trifluoromethylcoumarin cleavage activity and in situ poly(ADP-ribose) polymerase cleavage. Caspase activation coincided with the induction of apoptosis and capsid cleavage to the 40 kDa fragment. An in vitro cleavage assay, using recombinant human caspases and in vitro-derived FCV capsid protein, revealed that caspase-2, and to a lesser extent caspase-6, cleaved the capsid protein to generate a 40 kDa fragment. Taken together, these results suggest that FCV triggers apoptosis within infected cells and that caspase-induced capsid cleavage occurs concomitantly with apoptosis. The possible role of capsid cleavage in the pathogenesis of FCV infection is discussed.
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Affiliation(s)
- Naema Al-Molawi
- School of Biomedical and Life Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
| | - Victoria A Beardmore
- School of Biomedical and Life Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
| | - Michael J Carter
- School of Biomedical and Life Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
| | - George E N Kass
- School of Biomedical and Life Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
| | - Lisa O Roberts
- School of Biomedical and Life Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK
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23
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Woolaway KE, Lazaridis K, Belsham GJ, Carter MJ, Roberts LO. The 5' untranslated region of Rhopalosiphum padi virus contains an internal ribosome entry site which functions efficiently in mammalian, plant, and insect translation systems. J Virol 2001; 75:10244-9. [PMID: 11581392 PMCID: PMC114598 DOI: 10.1128/jvi.75.21.10244-10249.2001] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Rhopalosiphum padi virus (RhPV) is one of several picorna-like viruses that infect insects; sequence analysis has revealed distinct differences between these agents and mammalian picornaviruses. RhPV has a single-stranded positive-sense RNA genome of about 10 kb; unlike the genomes of Picornaviridae, however, this genome contains two long open reading frames (ORFs). ORF1 encodes the virus nonstructural proteins, while the downstream ORF, ORF2, specifies the structural proteins. Both ORFs are preceded by long untranslated regions (UTRs). The intergenic UTR is known to contain an internal ribosome entry site (IRES) which directs non-AUG-initiated translation of ORF2. We have examined the 5' UTR of RhPV for IRES activity by translating synthetic dicistronic mRNAs containing this sequence in a variety of systems. We now report that the 5' UTR contains an element which directs internal initiation of protein synthesis from an AUG codon in mammalian, plant, and Drosophila in vitro translation systems. In contrast, the encephalomyocarditis virus IRES functions only in the mammalian system. The RhPV 5' IRES element has features in common with picornavirus IRES elements, in that no coding sequence is required for IRES function, but also with cellular IRES elements, as deletion analysis indicates that this IRES element does not have sharply defined boundaries.
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Affiliation(s)
- K E Woolaway
- School of Biomedical and Life Sciences, University of Surrey, Guildford GU2 7XH, United Kingdom
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24
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Roberts LO, Boxall AJ, Lewis LJ, Belsham GJ, Kass GE. Caspases are not involved in the cleavage of translation initiation factor eIF4GI during picornavirus infection. J Gen Virol 2000; 81:1703-7. [PMID: 10859375 DOI: 10.1099/0022-1317-81-7-1703] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Infection of cells by many picornaviruses results in the rapid inhibition of cellular protein synthesis due to cleavage of the translation initiation factor eIF4G. The poliovirus (PV) 2A and foot-and-mouth disease virus (FMDV) L proteases are each sufficient to mediate this cleavage, but the cleavage mechanism may be indirect, involving an unidentified cellular protease(s). eIF4G is also targetted for cleavage by caspase-3 during apoptosis. Here, it is shown that caspase inhibitors do not inhibit the cleavage of eIF4GI during PV or FMDV infection. Similarly, in transient-expression studies, the cleavage of eIF4GI induced by PV 2A or FMDV L was unaffected by these inhibitors. Furthermore, the cleavage of eIF4GI was observed in PV-infected MCF-7 cells lacking caspase-3. These data, and the fact that induction of apoptosis yields different eIF4GI cleavage fragments, indicate that caspases do not have a major role in the cleavage of eIF4GI during PV or FMDV infection.
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Affiliation(s)
- L O Roberts
- School of Biological Sciences, University of Surrey, Guildford, Surrey GU2 5XH, UK.
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25
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Roberts LO, Seamons RA, Belsham GJ. Recognition of picornavirus internal ribosome entry sites within cells; influence of cellular and viral proteins. RNA 1998; 4:520-9. [PMID: 9582094 PMCID: PMC1369636 DOI: 10.1017/s1355838298971989] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
The ability of different picornavirus internal ribosome entry site (IRES) elements to direct initiation of protein synthesis has been assayed in different cell lines in the presence and absence of viral proteases that inhibit cap-dependent protein synthesis. Reporter plasmids that express dicistronic mRNAs, containing different IRES elements, with the general structure CAT/IRES/LUC, have been assayed. In each plasmid, the CAT sequence encodes chloramphenicol acetyl transferase and the LUC sequence encodes luciferase. The poliovirus (PV) 2A protease and the foot-and-mouth disease virus (FMDV) Lb protease induce the cleavage of the translation initiation factor elF4G and hence inhibit the activity of the cap-binding complex, elF4F. In human osteosarcoma (HTK-143) cells, each of the various IRES elements functioned efficiently. In these cells, the co-expression of the viral proteases severely inhibited the expression of CAT, but the proteases had little effect on the activities of the various IRES elements. In contrast, in baby hamster kidney (BHK) cells, the efficiencies of the different IRES elements varied significantly, whereas, in normal rat kidney (NRK) cells, each of the IRES elements was relatively inefficient. In both BHK and NRK cells, the activities of those IRES elements that functioned inefficiently were strongly stimulated by the co-expression of the PV 2A or FMDV Lb proteases. This stimulation was independent of the loss of cap-dependent protein synthesis and was not achieved by the co-expression of the C-terminal fragment of elF4G. The results suggest that the PV 2A and FMDV Lb proteases induce the cleavage of another cellular protein, in addition to elF4G, which influences IRES function.
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Affiliation(s)
- L O Roberts
- BBSRC Institute for Animal Health, Woking, Surrey, United Kingdom
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26
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Roberts LO, Belsham GJ. Complementation of defective picornavirus internal ribosome entry site (IRES) elements by the coexpression of fragments of the IRES. Virology 1997; 227:53-62. [PMID: 9007058 DOI: 10.1006/viro.1996.8312] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Mutant forms of the encephalomyocarditis virus (EMCV) internal ribosome entry site (IRES) have been produced and shown to be severely defective in directing internal initiation of protein synthesis within cells using the vaccinia/T7 RNA polymerase system. Mutants in different regions of the IRES were complemented in trans by coexpression of the intact EMCV IRES but not by coexpression of the related IRES elements from Theiler's murine encephalomyelitis virus (another cardiovirus) or from foot-and-mouth disease virus. Distinct, truncated regions of the EMCV IRES, insufficient to direct internal initiation, were also shown to complement defective EMCV IRES elements. It was necessary for the complementing molecule, whether truncated or full length, to be expressed in the positive sense orientation. RT-PCR analysis provided no support for the idea that any recombination event was responsible for the complementation. The data suggest that multiple activities are performed by distinct functional entities within the IRES in the process of internal initiation of protein synthesis. At least some of these different functions may be achieved by different molecules acting in trans.
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Affiliation(s)
- L O Roberts
- BBSRC Institute for Animal Health, Pirbright, Woking, Surrey, GU24 ONF, United Kingdom
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